Acoustic data will be derived from utterances of children recorded in their homes at two week intervals over the period from birth to five years of age. Sound spectrograms and computer-implemented Fourier analysis and waveform measurements will be used to derive formant frequency patterns for both vowels and consonants, burst frequencies for stop consonants, durations of phonetic segments and words and fundamental frequency contours. We will also use psychoacoustic tests when appropriate to assess the functional value of various acoustic events as cues to phonetic and phonologic contrasts. We will in particular address the following questions: (1) therole of duration and formant frequency pattern as independent cues for vowels in English - does the child acquire the phonetic features, across all members of a phonetic class of does the child acquire the individual phonetic elements? (2) syntactically conditioned word duration; (3) the status of "invarient" cues that include the stop bursts versus encoded formant frequency transitions to ee if either cue can be regarded as "primary"; (4) thestart of work acquisition with reference to the gradual develpment of phonetic ability in the child; (5) the acquisition of intonation and its relation to syntactic structure; (6) the role of context in "phonetic" translation of the speech of young children.